Quite obviously, a 13A fuse is wholly imappropriate for a cable rated at 10A, and that would fail it instantly. The plug should be fitted with a lower value fuse.

The PAT guidance for extension cables says that they must always be three core (LNE) and should not exceed 12 metres in length for core diameters of 1.25mm2, 15m for 1.5mm2 and 25m for 2.5mm2. Smaller cable core diameters are not specified as far as I know, although where the cable length is longer than those listed above the cable can be used if protected by a 30mA RCD.

The 25m, 2.5mm2 extension cable should be fed via a 60309-2 (16A) plug by the way, rather than the standard BS1363 (13A) plug.

Your 10A cable probably has core diamters of about 1mm2, which is outside the PAT guidance values and so I can see why someone ticking the boxes might fail it on a PAT test.

You don't say how long your extension reels are, or whether they have built in RCDs... both things would affect the test.

However, if the extension cable is less than about 10m and/or has a built-in RCD then I think it would probably be okay assuming a sensible size of fuse in the plug.

The plug fuse is there to protect the cable and nothing else. If the cable is rated at 10A then it should have a maximum ten amp fuse in the plug. It really isn't rocket science. Putting a 13 amp fuse in the plug means that the cable is no longer adequately protected.

The query is over this 'cut out' device which I presume is in the plug board section. If that is a simple current overload device then it is acting in the same way as the fuse to protect the cable, and that being the case it could be argued that the size of fuse is no longer relevant -- which is what your quote seems to suggest.

However, you are then totally reliant on the cut-out device operating to protect the cable and that would require appropriate certification before it would pass a PAT test. Fuses are approved, and a 10A fuse will pass the test regardless of the action (or not) of the thermal cut out.

On the other hand, if it is an integral RCD device then it offers no specific protection for the cable and we're back to needing a correctly rated fuse.

And then we have the issue of cable length, which as I explained above, if over a set length for the cable cross-sectional area must be protected with an RCD.

So the best course of action as I see it, is to have a discussion with your PAT testing company to establish exactly why the extensions reels failed -- they have to log the reason as part of the test -- and to agree on a plan of action to render them usable... which I suspect will mean fitting 10A fuses and RCDs in the plug-ends.

Thanks Hugh - I really appreciate your advice and knowledge. I was going to call the PAT tester anyway, but just needed to be clear about our side of things before they started talking Amps and Ohms at me!

The Bunk wrote:Sounds like Hugh has answered the question but I work with a fully qualified (to 17th edition) Electrician so am happy to ask him anything on your behalf if needs be....

Thanks Bunk, and please do - I would appreciate as many opinions as possible. I think one of the problems surrounding this are the different issues that exist because I'm in a school. The fact that the very same extension reel passed last year, but not this year, is a good example.

I think ultimately I am going to just send them all back to the company and buy different ones - but my problem now is just not knowing which ones are going to pass? I would never have thought the ones I did buy wouldn't be suitable, considering they are from a well known supplier, etc. But school rules seem to be different.

Exactly the same rules apply to all -- offices, schools, factories, hospitals and so on -- but there is a degree of application in the rules and not everyone interprets things in quite the same way.

Added to which, although the person doing the PAT must be a 'competent person' my own experience on the receiving end has indicated that some are more competent than others!

Another common problem is that some testing units provide a simple pass-fail indication which some testers take as gospel. However, there are situations where a fail indication doesn't actually mean fail -- and that could be what's happened in your case.

For example, the earth continuity requirement (for a Class 1 device, which an extension cable would be classed as) is for a resistance in the protective earth (cpc) path of not more than 0.1 ohms. And the simple pass-fail testers have that resistance as their test threshold. Any more than 0.1 ohms and they light up the fail flag. End of story.

However, long mains cables have a certain resistance due to their length and cross-sectional area. The longer the cable, the higher the resistance. That's the real world. So a long cable is quite likely to have a resistance rather greater than 0.1 ohms perfectly legitimately.

The actual PAT earth continuity requirement is 0.1+R ohms where R is a value determined by the cross-sectional area and the length of the cable concerned. It's all documented and all you have to do is measure the cable and look up the allowed value... but the simple testers have no facility to account for this extra R, and so issue a fail flag.

A competent tester would work out the actual permitted resistance for the cable and note the measured reading from the test unit to see if the latter is less than the former... in which case the cable passes despite getting a fail flag from the automated PAT unit.

As I said, some PAT technicians might not bother to do the sums and fail things on the basis of what the machine says!

Another problem I have though, is because the PAT tester failed things, added to that the majority of people in the school don't understand the rules that govern becoming a PAT tester (the fact that you and I could do it), once the school sees 'fail', they just assume it's gospel, and won't pay to have it re-tested. I'm scuppered really. It's not just about these extension reels, the PAT tester took a few other things from my store room, and it's proving tricky to get them back without an actual electrician giving it the go ahead. It doesn't seem to matter what I say.

geefunk wrote:once the school sees 'fail', they just assume it's gospel, and won't pay to have it re-tested.

The person doing the test has to have recorded the test result values and why the extension cable failed. A copy of these test results should be given to the 'responsible person' in your establishment.

If the extension cable failed because of an inappropriate fuse or the lack of an RCD, you can easily remedy that and return the cables to service.

If it has failed because or poor earth continuity, the test report should indicate that a proper resistance calculation was included in assessing the earth continuity. If that wasn't done the tester isn't competent and the company would be obliged to provide a free restest at the very least.

But this is all speculation on my part... The bottom line is that the responsible person in your establishment (or you acting as their representative) have to talk to the company and/or the actual testing person to find out precisely why these extention reels (and the other things) failed.

After all, they were bought in good faith from a reputable company that is not allowed by law to sell unsafe electrical products. Moreover these things represent a significant financial investment and were purchased specifically to facilitate what you do.

If they have failed a PAT then they have to be removed from use by law... fair enough... but you should be told why and whether they can be repaired or rendered usable.

Geefunk, I'm going to muddy the waters now I think, on reflection I would not have failed that extension lead.

I can't remeber whether it was the 15th or 16th edition regs, but the number of recommended fuses for BS1363 plugs was reduced. Out of 3A, 5A, 10A and 13A, the 5A and 10A fuses are "non-standard" and 3A and 13A are the "recommended" ones. This is disputed by some elecricians and it makes me uncomfortable.

The fuse value chosen is decided by the manufacturer of the equipment, determined by the feed cable size and the load characteristics of the equipment. For low current devices (below 700W a 3A fuse is usually used along with a 0.5 or 0.75 sqmm cable (a manufacturer may recommend a 5A fuse to prevent nusiance fuses blows based on surge or start-up currents). Above 700W a 13A fuses is usually recommended.

If your PAT tester was testing according to the 3rd edition of the IEE Code of Practice, he's actually deviated on two points, but I know why and I agree with him to a degree; I'll come back to this in a minute.

The IEE code of practice states for formal visual inspection: "The fuse recommended by the manufacturer should be fitted." and for combined inspection and testing: "inspect the plug as for a formal visual inspection".

In appendix VII, Checks to be made on a plug, a cable and an extension lead: "Check the rating of the fuse. The manufacturers recommendation should be followed." and "Most appliances up to about 700W should have a 3A fuse fitted (red). Appliances over about 700W should have a 13A fuse (brown) fitted."

I presume that Jo-Jo have chosen the 13A fuse to deal with heavy startup/inrush currents that might be present on some appliances used with the extension lead (remember not a fixed appliance-type here). A 13A fuse should protect a 1sqmm lead against fire (if unwound) -it may get hot, but the fuse will blow before the cable melts. A 10A fuse would protect it better, but the 13A fuse is within regs.

I bet the reel is clearly marked with "Max rating 10A" and "Do not use above nn Amps unless fully unwound", thus placing clear duty of care on the user to keep within safe limits

I would pass this item, but put a note in the results that a 10A fuse would be safer unless nusiance blowing is a problem. Being a Jo-Jo, I bet it also has an integral overcurrent breaker that will trip if more than 10A constant current is drawn (different time characteristics to the fuse to allow for transient currents). I do worry about 13A fuses in 0.75 sqmm (I just fit 5A and record it) or 1.0 sqmm IEC (kettle) leads though, as you never know which is as supplied and which is just user replaced.

Sorry if this appears confusing, but I hope there is enough info to take your PAT tester to task with this item. If he's failed it on a another aspect, that would be a different matter though.

I have an older Jo Jo cable which is probably similar. In an industrial situation (like a school), the fuses have to be rated for the worst case situation. In that case it should be the rating of the cable when fully wound inside the case. Being cased, the temperature rise is probably going to be even higher than if it was an open reel so the fuse must be even more conservatively rated. The built in cut out is at the socket end of the cable so it will do nothing to protect the cable if there is a problem. If you want the cable to pass then just fit an appropriate fuse (probably 3 or 5 amps) and retest.

In future don't buy an extension lead with less than 13A capacity when fully wound.

It discusses maximum lengths from the perspective of voltage drop for specific cable CSAs, and requires cables over those prescribed lengths to be protected by RCDs. Your extension reel certainly falls into that category.

Clearly, the cable should also be protected in some way to ensure it doesn't carry excess current -- and that's what the plug fuse and/or thermal cutout are for.

Despite the current standards not mentioning the 10A fuse, as geefunk states, it is still a properly certified value under BS1362, and personally I would fit a 10A fuse or lower to provide additional safety to augment the reel's own thermal cut-out protection. In fact, I'd fit an RCD plug too...

But whatever, I think he's wrong to have failed them purely on the basis of cable diameter.

I would tend to agree with you Hugh, but the IEE PAT guide says what the manufacturer recommends, and then only states two fue sizes in its appendix. A ten Amp fuse would would also stop someone pulling 13A through it continually (it would blow within half an hour or shorter).

By the Guide, a 10A extension lead is permissible up to 10m in length, providing it has an earth conductor and that is within its required minimum resistance (0.1+R, =0.295 ohms). I make my leads from 1.5 (and 2.5) sqmm so I can have them longer and suffer less volt drop.

Having to put a 5 or even 3 Amp fuse to protecr against heavy use with the cable unwound does seem to be bordering on the ridiculous though -maybe the reels should be locked away and only used with supervision?

-saying that, I have had to fail extension reels because the cable was a solidified lump in the middle and wouldn't un-peel off the drum (hippy arts group)

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Edit: of course if the PAT tester is testing to a school or local authority schedule or policy (additional to the IEE guide) then the 10A reel may be outside its scope. I've had additional conditions place upon testing for appliances use by young people (labels and fuses) so this would be feasable...

One other point, in something like one of those jojo reels you could argue that the fuse exists to protect the cable in the event of a short circuit, the trip providing the limit on I^2T let through required to prevent the cable melting on the difference between 10A and 13A.

I would have passed the thing.

After all if you had an appliance internally fused or breakered at 10A, you would not think twice about feeding it from a 13A fuse, and this is pretty much that situation if you squint just right.

Now that said, most DIY shop extension reels are crap, but it is not the testers job to be the arbiter of quality, only of 'is it safe at the moment'.

Many years ago, as part of my engineering HNC I took a course and gained a qualification to instal 3 phase and single phase conections (to BS 1363 if my memory serves) the exam comprised being given a length of flex and a plug. You had to strip the flex and wire the plug then hand it in to the examiner, who then took it apart and checked for stray strands, correct installation and stripped lengths of cable etc.

On the table you had all the correct tools and a few rogue ones, such as a stanley knife. If you used the wrong tools and put a cut in any of the shielding you failed. Whenever I wired something I tried to maintain those standards to make sure what I did was safe.

However, being a cautious sole, I would be much happier to give my kit to somebody else to PAT test and let them take the responsability. Even if the problem was caused by somebody abusing my kit, I would have the legal backing of having put a system of protection in place, which could mean protection from a large fine. A fine that I suspect would be many times that of the cost of PAT testing.